This HVAC floor plan sample shows the ventilation duct system layout.
"Ducts are used in heating, ventilation, and air conditioning (HVAC) to deliver and remove air. The needed airflows include, for example, supply air, return air, and exhaust air. Ducts commonly also deliver ventilation air as part of the supply air. As such, air ducts are one method of ensuring acceptable indoor air quality as well as thermal comfort.
A duct system is also called ductwork. Planning (laying out), sizing, optimizing, detailing, and finding the pressure losses through a duct system is called duct design." [Duct (flow). Wikipedia]
The HVAC floor plan example "Ductwork layout" was created using the ConceptDraw PRO diagramming and vector drawing software extended with the HVAC Plans solution from the Building Plans area of ConceptDraw Solution Park.